This invention relates to a multicolor image developing device to develop a latent image formed on a light-sensitive drum, an image carrier, by a plurality of developing means containing respective color developing agent to obtain color copies by an electrophotographic method.
Many methods and devices have been proposed to obtain a color image using electrophotographic methods. For instance, as disclosed in the official bulletin of Japanese Patent Publication Open to Public Inspection No. 100770/1986 (hereinafter referred to as Japanese Patent 0.P.I. Publication), there is a method to obtain color copies by forming and developing latent images on a light-sensitive drum according to number of separated colors of the original copy image, transferring them to a transfer drum every time of development to form a multiple color image on the transfer drum, and then transferring it on recording paper to obtain color copies. Devices using this method should have a transfer drum which is sized to enable to transfer an image of one sheet on its periphery surface in addition to the light-sensitive drum and therefore the device becomes inevitably large in size and complicated in structure.
There is another method of obtaining multiple color copies by forming and developing latent images on a light-sensitive drum according to the number of separated colors of the original copy image and transferring them on a transfer material every time of developing to obtain multiple color copies as disclosed in the official bulletin of Japanese Patent 0.P.I. Publication No. 149972/1986. It is difficult by this method to place one color image upon another with high accuracy and high quality color copies cannot be obtained.
There is another method of obtaining a color image by repeating formation of a latent image and development with color toner on a light-sensitive drum according to the number of separated colors of the original copy image, placing a color toner over another color toner image, and then transferring them onto a copy paper.
This basic multiple color image forming process has been disclosed in the official bulletin of Japanese Patent 0.P.I. Publication Nos. 75850/1985, 76766/1985, 95456/1985, 158475/1985, and others by the applicant of this invention.
In such multicolor image developing devices which obtain a color image by superimposing a color toner upon another color toner image, multiple developing devices containing toner of different colors are arranged on the periphery of a light-sensitive drum and generally the light-sensitive drum is rotated several turns to develop the latent image on it and obtain a color image.
In this case, the light sensitive drum should have a circumference longer at least than a length of the original document. For instance, for the maximum recording body of the B4 form (364.times.257/mm), the drum diameter should be about 130 mm.phi. including the allowance required in the image forming process.
According to the study by the applicant of this invention, as described in details in the specification of Japanese Patent 0.P.I. Publication No. 229165/1987, since the latent image written by a writing means on the light-sensitive drum is transferred after a developed image is placed one upon another, a cleaning means should be separated from the light-sensitive drum periphery surface during image formation and the cleaning means is brought in sliding contact with the light-sensitive drum periphery surface only after the transfer process. At this time, it gives influence on the rotation of the light-sensitive drum and if writing by the writing means is being continued at this time, images to be placed upon another are deviated and the image quality is deteriorated. Therefore, the light sensitive drum diameter should be sized with sufficient allowance. The same is applicable to development. Developing by the multiple developing means provided on the periphery of the light-sensitive drum applying developing bias at the same time causes a difference from the point where the independent developing means conducts development and is undesirable. The size of the image carrier drum is determined based on these conditions and a large diameter drum is required as described above. In multicolor image developing devices in which color images are placed upon one another on a light-sensitive drum, such developing means which conduct development with a traditional magnetic brush in contact with an image carrier cannot be used. The applicant of this invention made it possible to provide a multicolor image developing device in which toner images are placed upon one another on an image carrier using the non-contact developing method which was disclosed in the official bulletin of Japanese Patent 0.P.I. Publication No. 147652/1982 and others. As for general duplicators, it is proposed to install a light-sensitive drum, developing equipment and cleaner integrally to a supporting member to facilitate substitution, repair, etc. of each unit as disclosed in the official bulletin of Japanese Patent 0.P.I. Publication No. 54392/1983. To cope with monochrome, a disposable composition unifying them in one unit for easy replacement is disclosed in the official bulletin of Japanese Patent 0.P.I. Publication No. 154255/1982. However, none improve them to cope with multiple color image developing devices which have multi color or full color developing devices, improving the maintenance or working efficiency.
When multiple developing devices are arranged on the periphery of a light-sensitive drum, toner is dispersed more in the equipment rather than in general duplicating machines and service, maintenance, and other jobs should be conducted more often.
However, in multicolor image developing devices in which toner images are placed upon one another on an image carrier as described above, the equipment is complicated and large in size, especially in multiple developing devices which keep highly accurate gap dimensions to the light sensitive drum surface respectively, and handling multiple developing devices is complicated. Thus expecting easier service, maintenance, and other jobs is almost impossible.
Especially in developing devices using a 2-component type developing agent, change of developing agent, cleaning of dispersed toner, and other indispensable maintenance treatment are required unless they are of the disposable type. In addition, cleaning and replacement of the density sensor, cleaning of the bias contact point or armature, and other various maintenance jobs are necessary. Especially handling multiple developing devices in order to form color images makes such maintenance jobs more complicated. Any method to make them easier has not been provided.
In summary, the following problems can be cited:
(1) In the color image forming apparatus, described above, such as overlapping color image and other multiple color image developing devices, an arrangement, form or other conditions of an individual developing device vary depending on the structure of equipment, which caused problems such that the light-sensitive body is damaged when it is substituted or the developing device is pulled out to change the developing agent. In another case, in order to solve the problem that toner image on a light-sensitive body after being developed in a certain color may be scraped by a developing device of another color toner and resultantly the toner image is disturbed or the colors were mixed, each developing device should have had a touching and separating mechanism. In addition, there were mechanical and time problems such as switching of bias, etc. Their structure is complicated, multiple units should be handled for operation and maintenance requiring complicated jobs, a large number of parts are required, and resultantly there is a tendency that reliability is inferior.
(2) On the other hand, there are various methods to conduct development at a same point by turning a developing device disposed at a specified position of a rotatable body by a specified angle for each developing color, which is known as a rotary developing device. These methods are difficult to obtain positioning accuracy during the rotating operation. Especially in the case of non-contact development, the positioning mechanism for the gap (Dsd) between the image carrier and developing agent carrier is complicated and accuracy is difficult to obtain or speed-up is difficult due to the time restriction required for rotation, and there are various other problems.
(3) In addition, variation of developing characteristics due to variation of Dsd caused by the variation of the drum diameter resulting from changes in the temperature within the machine or variation of Dsd caused by influence of internal or external vibration, impact, etc. causes deterioration of image quality conjointly with the size of the light-sensitive drum. Actually, variation of Dsd requires accuracy of about '0.02-0.03 mm, while rotating eccentricity of the drum central axis is usually about .+-.0.005-0.01 and the gap between the drum surface after being installed to the equipment main body and developing device varies about .+-.0.1-0.3 mm. Also expansion and contraction of about .+-.0.01-0.02 mm is caused in a current drum made of aluminum as the major material due to variation of temperature in the machine when the equipment is used in a temperature of 5-35.degree. C.
Along with the electric potential variation at the time of development as described above in (2), color mixture, color balance and other adverse influences are given to the image quality.
Other major problems which this invention intends to solve are as follows:
In the developing devices described above, replenishing hoppers to replenish toner respectively are often incorporated on the side of the group of developing devices in the equipment main body usually and therefore each developing device and corresponding replenishing hopper should be connected within the confined space. For the purpose of supplementing toner to replenishing hopper, an opening door or the like to insert a developing agent cartridge should be specifically provided on the top or side of the equipment main body. Thus, disadvantages such as high manufacturing cost and complicated handling for users were unavoidable. Especially, if realizing an in image developing devices which are composed so that the group of the developing devices are installed integrally together with an image carrier to a supporting member or a housing member which can be pulled out, the group of the developing devices can be removed easily from the equipment main body by pulling out the supporting member for very simplified maintenance and inspection, however, if the group of the replenishing hoppers should be removed individually from the equipment main body independently of the group of developing devices, their maintenance and inspections are not easy.
An object of this invention is to provide a multicolor image developing device which is composed so that the group of replenishing hoppers are installed within space with allowance and the group of the replenishing hoppers can be also removed from the equipment main body at the same time as pulling out of the supporting member housing the developing devices and the image carrier therein. When installing a replenishing hopper to the supporting member, it is the most rational to install it to the front of the supporting member from the view point of the necessity of securing sufficient large capacity, layout of the connecting mechanism, or installation and operation of the developing agent cartridge. For this reason, replenishing hoppers containing a specific color of toner respectively are provided in a row in the lateral direction on the front of the supporting member and each replenishing hopper vessel is square shorter in the longitudinal direction and slightly longer in the lateral direction in many cases for the purpose of making the depth of the equipment main body compact. Therefore, because of the vessel shape, the opening/closing door of the toner replenishing port will be unavoidably opened in the lateral direction and resultantly the vessel of another adjacent replenishing hopper interferes with it in some cases.
Especially in image developing devices of the type to incline the replenishing hopper at a certain angle frontward when replenishing toner, opening or closing the lid in the longitudinal direction is impossible. The second object of this invention is to provide an image developing device which can open or close the replenishing port without being hindered by an adjacent replenishing hopper and can replenish toner easily by installing a developing agent cartridge to each replenishing hopper arranged in a row in the lateral direction, as the result of having solved and improved this point.